Halogenated ethylbenzenes are known as important intermediate products of agricultural chemicals, etc. Especially m-chloroethylbenzene (hereinafter chloroethylbenzene is abbreviated as CEB) or m-bromoethylbenzene (hereinafter bromoethylbenzene is abbreviated as BEB) is expected as a raw material of agricultural chemicals with specific bioactivity as an isomer different from p- and o-isomers.- CEB or BEB is mainly produced by aromatic ring chlorination or bromination reaction of ethylbenzene, but since the reaction is very strong in ortho-orientation and para-orientation, the m-isomer can be produced only in a small amount.
Therefore, CEB and BEB isomerization methods have an important technical significance. Conventionally known isomerization reactions for these compounds include a method of using aluminum chloride, etc. as a catalyst disclosed in Olah. G. A. J. Org. CHEM. 27, 3464 (1962), a method of using HF--BF.sub.3 as a catalyst disclosed in Japanese Patent Laid-Open (Kokai) 46-11809, etc. Furthermore, Idar A. Acta Chemica Scandinavica B39,437 (1985) describes a chloroethylbenzene isomerization reaction using a mordenite-type zeolite. Furthermore, methods for isomerizing a halogenated toluene using a zeolite as a catalyst are disclosed in Japanese Patent Laid-Open (Kokai) Nos. 57-40428, 85330, 163327 and 7-309792.
However, in the isomerization reactions of halogenated ethylbenzenes, it has been difficult to efficiently isomerize using conventional catalysts such as aluminum chloride and HF--BF.sub.3 since the disproportionation reaction accompanying the de-ethylation reaction or intermolecular migration of ethyl groups is likely to occur, unlike the isomerization reactions of halogenated toluenes. Furthermore, because of such problems as the enormous use of catalyst for isomerization, corrosion of reactor and environmental issue in the treatment of waste catalyst, the conventional methods are not efficient. The isomerization reaction using a mordenite catalyst is less in these problems, but has such a disadvantage that since the catalyst life is short, the zeolite must be regenerated after hundreds of hours. So, a method for more efficiently obtaining a desired halogenated ethylbenzene is strongly demanded.
For separation of halogenated ethylbenzene isomers, since the halogenated ethylbenzene isomers are not so different in boiling point, a precision distillation column with a very large number of stages is necessary for separating them. So, it has been difficult to efficiently separate a m-halogenated ethylbenzene at high purity.
As methods for separating the isomers of chlorotoluene structurally different from halogenated ethylbenzenes of the present invention, Japanese Patent Publication (Tokko) No. 37-5155 discloses an adsorption separation method using a zeolite X as the adsorbent, and Japanese Patent Laid-Open (Kokai) Nos. 57-31627, 35528 and 91933 disclose adsorption separation methods using a K ion exchanged zeolite Y as the adsorbent. These methods can separate the m-isomer from the p-isomer by adsorption, but cannot separate the m-isomer from the o-isomer, and m-chlorotoluene cannot be singly separated as an extract component or raffinate component. Furthermore, Japanese Patent Laid-Open (Kokai) Nos. 58-131923 and 59-176223 disclose m-chlorotoluene separation methods using an Ag and K ion exchanged zeolite Y or a Na and Cu ion exchanged zeolite Y as the adsorbent, and these methods can separate m-chlorotoluene as a raffinate component. However, as far as the inventors examined, these adsorbents could little separate m-CEB. As described so far, no method for adsorbing and separating a halogenated ethylbenzene has been known at all, and there has been no idea of attempting it at all.